Luggage and bags:
I usually pack a nice duffle bag inside of my suticase for souveniers. You might think about a nice canvas tote that folds flat too, if you like to shop. Some of the groceries charge for bags.
Clothing/Shoes/Weather Gear: Comfy shoes for walking around in will make your trip much nicer as well as a nice rain jacket and an umbrella! I love wearing sweaters on the cooler days or over another shirt incase the day warms up, you can just take off the sweater. I have found that dressing in layers is a good thing in Ireland. Kinsale has some wonderful gourmet restaurants and sometimes it is just nice to get to dress nice for the occasion. So bring a couple of nice outfits for dining out in.
Toiletries and Medical Supplies: Lip balm will be your best friend for those cool breezy days as well as a moisterizer for your hands and face. If your hair tends to frizz easily, I suggest you bring a hair product for that with you as well.
Photo Equipment: Definately bring your camera! If it requires film, bring that as well, it can be pricey in the shops. Bring extra batteries as well. If it is digital, be sure to bring a nice sized memory card because you will be taking many wonderful pictures!